Flowable materials such as liquids, powders, and other materials that, in the aggregate, conform to the shape of a container from the bottom up, are often stored in containers. Such containers can assume many forms including silos, tanks, bladders, boxes, jars, bottles, cartridges, tubes, vials, cavities, and tubes. When such containers are remotely located, concealed, or in motion, or where the container wall is rigid and/or opaque, it is often desirable to equip the container (or the apparatus receiving the container) with a sensor that can detect the level of flowable material in the container.
As used herein, the term “level” refers to a vertical position of the flowable material's top surface, and depending on the shape of the container, and on the topography, motion, and composition of the top surface, the position may be approximate (e.g., anywhere in a range between highest and lowest points on the top surface), averaged (e.g, over spatial and time dimensions), or correspond with a particular position characteristic of the top surface (e.g, meniscus, topographic maximum, time-windowed minimum). Such variations are generally design options that, given suitable calibration, can be implemented at will by the designer of the level sensing system.
Traditional level sensor designs often require moving parts, which are vulnerable to friction, corrosion, and the accumulation of dirt or debris, each of which can vary the operation of the sensor in a way that introduces uncertainty into the measured level. Designs that do not require moving parts often rely on physical characteristics of the flowable material, and when such physical properties vary (e.g., due to changes in temperature), designs that fail to compensate for such variations are again susceptible to measurement uncertainty. Incorporating compensation for such effects typically contributes undesirable complexity and cost to the level sensing system.